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1 : dl 1.38 /*
2 : jsr166 1.71 * Copyright (c) 2003, 2006, Oracle and/or its affiliates. All rights reserved.
3 : jsr166 1.67 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 : dl 1.38 *
5 : jsr166 1.67 * This code is free software; you can redistribute it and/or modify it
6 :     * under the terms of the GNU General Public License version 2 only, as
7 :     * published by the Free Software Foundation. Sun designates this
8 :     * particular file as subject to the "Classpath" exception as provided
9 :     * by Sun in the LICENSE file that accompanied this code.
10 :     *
11 :     * This code is distributed in the hope that it will be useful, but WITHOUT
12 :     * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 :     * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 :     * version 2 for more details (a copy is included in the LICENSE file that
15 :     * accompanied this code).
16 :     *
17 :     * You should have received a copy of the GNU General Public License version
18 :     * 2 along with this work; if not, write to the Free Software Foundation,
19 :     * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 :     *
21 : jsr166 1.71 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 :     * or visit www.oracle.com if you need additional information or have any
23 :     * questions.
24 : dl 1.38 */
25 :    
26 :     package java.util;
27 : tim 1.1
28 :     /**
29 : jsr166 1.63 * An unbounded priority {@linkplain Queue queue} based on a priority heap.
30 :     * The elements of the priority queue are ordered according to their
31 :     * {@linkplain Comparable natural ordering}, or by a {@link Comparator}
32 :     * provided at queue construction time, depending on which constructor is
33 :     * used. A priority queue does not permit {@code null} elements.
34 :     * A priority queue relying on natural ordering also does not permit
35 :     * insertion of non-comparable objects (doing so may result in
36 :     * {@code ClassCastException}).
37 : dl 1.40 *
38 : dl 1.41 * <p>The <em>head</em> of this queue is the <em>least</em> element
39 :     * with respect to the specified ordering. If multiple elements are
40 :     * tied for least value, the head is one of those elements -- ties are
41 : jsr166 1.63 * broken arbitrarily. The queue retrieval operations {@code poll},
42 :     * {@code remove}, {@code peek}, and {@code element} access the
43 : dl 1.42 * element at the head of the queue.
44 : tim 1.14 *
45 : dl 1.41 * <p>A priority queue is unbounded, but has an internal
46 :     * <i>capacity</i> governing the size of an array used to store the
47 : dl 1.40 * elements on the queue. It is always at least as large as the queue
48 :     * size. As elements are added to a priority queue, its capacity
49 :     * grows automatically. The details of the growth policy are not
50 :     * specified.
51 : tim 1.2 *
52 : dl 1.50 * <p>This class and its iterator implement all of the
53 :     * <em>optional</em> methods of the {@link Collection} and {@link
54 : dl 1.52 * Iterator} interfaces. The Iterator provided in method {@link
55 :     * #iterator()} is <em>not</em> guaranteed to traverse the elements of
56 :     * the priority queue in any particular order. If you need ordered
57 : jsr166 1.63 * traversal, consider using {@code Arrays.sort(pq.toArray())}.
58 : dl 1.29 *
59 : jsr166 1.78 * <p><strong>Note that this implementation is not synchronized.</strong>
60 : jsr166 1.63 * Multiple threads should not access a {@code PriorityQueue}
61 :     * instance concurrently if any of the threads modifies the queue.
62 :     * Instead, use the thread-safe {@link
63 : dholmes 1.34 * java.util.concurrent.PriorityBlockingQueue} class.
64 : dl 1.29 *
65 : jsr166 1.63 * <p>Implementation note: this implementation provides
66 :     * O(log(n)) time for the enqueing and dequeing methods
67 :     * ({@code offer}, {@code poll}, {@code remove()} and {@code add});
68 :     * linear time for the {@code remove(Object)} and {@code contains(Object)}
69 :     * methods; and constant time for the retrieval methods
70 :     * ({@code peek}, {@code element}, and {@code size}).
71 : tim 1.2 *
72 :     * <p>This class is a member of the
73 : jsr166 1.65 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
74 : tim 1.2 * Java Collections Framework</a>.
75 : jsr166 1.63 *
76 : dl 1.7 * @since 1.5
77 : jsr166 1.63 * @author Josh Bloch, Doug Lea
78 : dl 1.45 * @param <E> the type of elements held in this collection
79 : tim 1.2 */
80 : jsr166 1.76 @SuppressWarnings("unchecked")
81 : tim 1.2 public class PriorityQueue<E> extends AbstractQueue<E>
82 : dl 1.47 implements java.io.Serializable {
83 : dholmes 1.11
84 : dl 1.31 private static final long serialVersionUID = -7720805057305804111L;
85 : dl 1.30
86 : tim 1.2 private static final int DEFAULT_INITIAL_CAPACITY = 11;
87 : tim 1.1
88 : tim 1.2 /**
89 : dl 1.55 * Priority queue represented as a balanced binary heap: the two
90 :     * children of queue[n] are queue[2*n+1] and queue[2*(n+1)]. The
91 :     * priority queue is ordered by comparator, or by the elements'
92 :     * natural ordering, if comparator is null: For each node n in the
93 :     * heap and each descendant d of n, n <= d. The element with the
94 :     * lowest value is in queue[0], assuming the queue is nonempty.
95 : tim 1.2 */
96 : tim 1.16 private transient Object[] queue;
97 : tim 1.1
98 : tim 1.2 /**
99 :     * The number of elements in the priority queue.
100 :     */
101 :     private int size = 0;
102 : tim 1.1
103 : tim 1.2 /**
104 :     * The comparator, or null if priority queue uses elements'
105 :     * natural ordering.
106 :     */
107 : tim 1.16 private final Comparator<? super E> comparator;
108 : tim 1.2
109 :     /**
110 :     * The number of times this priority queue has been
111 :     * <i>structurally modified</i>. See AbstractList for gory details.
112 :     */
113 : dl 1.5 private transient int modCount = 0;
114 : tim 1.2
115 :     /**
116 : jsr166 1.63 * Creates a {@code PriorityQueue} with the default initial
117 : dl 1.52 * capacity (11) that orders its elements according to their
118 :     * {@linkplain Comparable natural ordering}.
119 : tim 1.2 */
120 :     public PriorityQueue() {
121 : dholmes 1.11 this(DEFAULT_INITIAL_CAPACITY, null);
122 : tim 1.1 }
123 : tim 1.2
124 :     /**
125 : jsr166 1.63 * Creates a {@code PriorityQueue} with the specified initial
126 : dl 1.52 * capacity that orders its elements according to their
127 :     * {@linkplain Comparable natural ordering}.
128 : tim 1.2 *
129 : dl 1.52 * @param initialCapacity the initial capacity for this priority queue
130 : jsr166 1.63 * @throws IllegalArgumentException if {@code initialCapacity} is less
131 :     * than 1
132 : tim 1.2 */
133 :     public PriorityQueue(int initialCapacity) {
134 :     this(initialCapacity, null);
135 : tim 1.1 }
136 : tim 1.2
137 :     /**
138 : jsr166 1.63 * Creates a {@code PriorityQueue} with the specified initial capacity
139 : tim 1.2 * that orders its elements according to the specified comparator.
140 :     *
141 : dl 1.52 * @param initialCapacity the initial capacity for this priority queue
142 : jsr166 1.63 * @param comparator the comparator that will be used to order this
143 :     * priority queue. If {@code null}, the {@linkplain Comparable
144 :     * natural ordering} of the elements will be used.
145 :     * @throws IllegalArgumentException if {@code initialCapacity} is
146 : dl 1.52 * less than 1
147 : tim 1.2 */
148 : dl 1.52 public PriorityQueue(int initialCapacity,
149 : dholmes 1.23 Comparator<? super E> comparator) {
150 : dl 1.55 // Note: This restriction of at least one is not actually needed,
151 :     // but continues for 1.5 compatibility
152 : tim 1.2 if (initialCapacity < 1)
153 : dholmes 1.15 throw new IllegalArgumentException();
154 : dl 1.55 this.queue = new Object[initialCapacity];
155 : tim 1.2 this.comparator = comparator;
156 : tim 1.1 }
157 : jsr166 1.56
158 : dl 1.22 /**
159 : jsr166 1.63 * Creates a {@code PriorityQueue} containing the elements in the
160 :     * specified collection. If the specified collection is an instance of
161 :     * a {@link SortedSet} or is another {@code PriorityQueue}, this
162 :     * priority queue will be ordered according to the same ordering.
163 :     * Otherwise, this priority queue will be ordered according to the
164 :     * {@linkplain Comparable natural ordering} of its elements.
165 : tim 1.2 *
166 : dl 1.52 * @param c the collection whose elements are to be placed
167 :     * into this priority queue
168 : tim 1.2 * @throws ClassCastException if elements of the specified collection
169 :     * cannot be compared to one another according to the priority
170 : dl 1.52 * queue's ordering
171 :     * @throws NullPointerException if the specified collection or any
172 :     * of its elements are null
173 : tim 1.2 */
174 : jsr166 1.70 @SuppressWarnings("unchecked")
175 : tim 1.16 public PriorityQueue(Collection<? extends E> c) {
176 : jsr166 1.70 if (c instanceof SortedSet<?>) {
177 :     SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
178 :     this.comparator = (Comparator<? super E>) ss.comparator();
179 :     initElementsFromCollection(ss);
180 :     }
181 :     else if (c instanceof PriorityQueue<?>) {
182 :     PriorityQueue<? extends E> pq = (PriorityQueue<? extends E>) c;
183 :     this.comparator = (Comparator<? super E>) pq.comparator();
184 :     initFromPriorityQueue(pq);
185 :     }
186 : dl 1.55 else {
187 : jsr166 1.70 this.comparator = null;
188 :     initFromCollection(c);
189 : tim 1.2 }
190 : dl 1.22 }
191 :    
192 :     /**
193 : jsr166 1.63 * Creates a {@code PriorityQueue} containing the elements in the
194 : dl 1.55 * specified priority queue. This priority queue will be
195 : dl 1.52 * ordered according to the same ordering as the given priority
196 :     * queue.
197 :     *
198 :     * @param c the priority queue whose elements are to be placed
199 :     * into this priority queue
200 : jsr166 1.63 * @throws ClassCastException if elements of {@code c} cannot be
201 :     * compared to one another according to {@code c}'s
202 : dl 1.52 * ordering
203 :     * @throws NullPointerException if the specified priority queue or any
204 :     * of its elements are null
205 : dl 1.22 */
206 : jsr166 1.70 @SuppressWarnings("unchecked")
207 : dl 1.22 public PriorityQueue(PriorityQueue<? extends E> c) {
208 : jsr166 1.70 this.comparator = (Comparator<? super E>) c.comparator();
209 :     initFromPriorityQueue(c);
210 : dl 1.22 }
211 : dholmes 1.18
212 : dl 1.22 /**
213 : jsr166 1.63 * Creates a {@code PriorityQueue} containing the elements in the
214 :     * specified sorted set. This priority queue will be ordered
215 : dl 1.52 * according to the same ordering as the given sorted set.
216 :     *
217 :     * @param c the sorted set whose elements are to be placed
218 : jsr166 1.63 * into this priority queue
219 : dl 1.52 * @throws ClassCastException if elements of the specified sorted
220 :     * set cannot be compared to one another according to the
221 :     * sorted set's ordering
222 :     * @throws NullPointerException if the specified sorted set or any
223 :     * of its elements are null
224 : dl 1.22 */
225 : jsr166 1.70 @SuppressWarnings("unchecked")
226 : dl 1.22 public PriorityQueue(SortedSet<? extends E> c) {
227 : jsr166 1.70 this.comparator = (Comparator<? super E>) c.comparator();
228 :     initElementsFromCollection(c);
229 :     }
230 :    
231 :     private void initFromPriorityQueue(PriorityQueue<? extends E> c) {
232 :     if (c.getClass() == PriorityQueue.class) {
233 :     this.queue = c.toArray();
234 :     this.size = c.size();
235 :     } else {
236 :     initFromCollection(c);
237 :     }
238 :     }
239 :    
240 :     private void initElementsFromCollection(Collection<? extends E> c) {
241 :     Object[] a = c.toArray();
242 :     // If c.toArray incorrectly doesn't return Object[], copy it.
243 :     if (a.getClass() != Object[].class)
244 :     a = Arrays.copyOf(a, a.length, Object[].class);
245 :     int len = a.length;
246 :     if (len == 1 || this.comparator != null)
247 :     for (int i = 0; i < len; i++)
248 :     if (a[i] == null)
249 :     throw new NullPointerException();
250 :     this.queue = a;
251 :     this.size = a.length;
252 : tim 1.1 }
253 :    
254 : dl 1.22 /**
255 : jsr166 1.63 * Initializes queue array with elements from the given Collection.
256 :     *
257 : dl 1.55 * @param c the collection
258 : dl 1.22 */
259 : dl 1.55 private void initFromCollection(Collection<? extends E> c) {
260 : jsr166 1.70 initElementsFromCollection(c);
261 :     heapify();
262 : jsr166 1.56 }
263 : dl 1.55
264 :     /**
265 : jsr166 1.70 * The maximum size of array to allocate.
266 :     * Some VMs reserve some header words in an array.
267 :     * Attempts to allocate larger arrays may result in
268 :     * OutOfMemoryError: Requested array size exceeds VM limit
269 :     */
270 :     private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
271 :    
272 :     /**
273 : dl 1.55 * Increases the capacity of the array.
274 :     *
275 :     * @param minCapacity the desired minimum capacity
276 :     */
277 :     private void grow(int minCapacity) {
278 : jsr166 1.68 int oldCapacity = queue.length;
279 : dl 1.55 // Double size if small; else grow by 50%
280 : jsr166 1.70 int newCapacity = oldCapacity + ((oldCapacity < 64) ?
281 :     (oldCapacity + 2) :
282 :     (oldCapacity >> 1));
283 :     // overflow-conscious code
284 :     if (newCapacity - MAX_ARRAY_SIZE > 0)
285 :     newCapacity = hugeCapacity(minCapacity);
286 : dl 1.55 queue = Arrays.copyOf(queue, newCapacity);
287 : dl 1.22 }
288 : dl 1.36
289 : jsr166 1.70 private static int hugeCapacity(int minCapacity) {
290 :     if (minCapacity < 0) // overflow
291 :     throw new OutOfMemoryError();
292 :     return (minCapacity > MAX_ARRAY_SIZE) ?
293 :     Integer.MAX_VALUE :
294 :     MAX_ARRAY_SIZE;
295 :     }
296 :    
297 : tim 1.2 /**
298 : dl 1.42 * Inserts the specified element into this priority queue.
299 : tim 1.2 *
300 : jsr166 1.63 * @return {@code true} (as specified by {@link Collection#add})
301 : dl 1.52 * @throws ClassCastException if the specified element cannot be
302 :     * compared with elements currently in this priority queue
303 :     * according to the priority queue's ordering
304 :     * @throws NullPointerException if the specified element is null
305 : tim 1.2 */
306 : dl 1.52 public boolean add(E e) {
307 :     return offer(e);
308 :     }
309 :    
310 :     /**
311 :     * Inserts the specified element into this priority queue.
312 :     *
313 : jsr166 1.63 * @return {@code true} (as specified by {@link Queue#offer})
314 : dl 1.52 * @throws ClassCastException if the specified element cannot be
315 :     * compared with elements currently in this priority queue
316 :     * according to the priority queue's ordering
317 :     * @throws NullPointerException if the specified element is null
318 :     */
319 :     public boolean offer(E e) {
320 :     if (e == null)
321 : dholmes 1.11 throw new NullPointerException();
322 :     modCount++;
323 : dl 1.55 int i = size;
324 :     if (i >= queue.length)
325 :     grow(i + 1);
326 :     size = i + 1;
327 :     if (i == 0)
328 :     queue[0] = e;
329 :     else
330 :     siftUp(i, e);
331 : dholmes 1.11 return true;
332 :     }
333 :    
334 : dl 1.40 public E peek() {
335 : jsr166 1.73 return (size == 0) ? null : (E) queue[0];
336 : tim 1.1 }
337 :    
338 : dl 1.52 private int indexOf(Object o) {
339 : jsr166 1.68 if (o != null) {
340 : dl 1.55 for (int i = 0; i < size; i++)
341 :     if (o.equals(queue[i]))
342 :     return i;
343 :     }
344 : dl 1.52 return -1;
345 :     }
346 :    
347 :     /**
348 :     * Removes a single instance of the specified element from this queue,
349 : jsr166 1.63 * if it is present. More formally, removes an element {@code e} such
350 :     * that {@code o.equals(e)}, if this queue contains one or more such
351 :     * elements. Returns {@code true} if and only if this queue contained
352 :     * the specified element (or equivalently, if this queue changed as a
353 :     * result of the call).
354 : dl 1.52 *
355 :     * @param o element to be removed from this queue, if present
356 : jsr166 1.63 * @return {@code true} if this queue changed as a result of the call
357 : dl 1.52 */
358 :     public boolean remove(Object o) {
359 : jsr166 1.68 int i = indexOf(o);
360 :     if (i == -1)
361 :     return false;
362 :     else {
363 :     removeAt(i);
364 :     return true;
365 :     }
366 : dl 1.52 }
367 : dholmes 1.11
368 : jsr166 1.56 /**
369 : dl 1.55 * Version of remove using reference equality, not equals.
370 : jsr166 1.59 * Needed by iterator.remove.
371 : jsr166 1.56 *
372 : dl 1.55 * @param o element to be removed from this queue, if present
373 : jsr166 1.63 * @return {@code true} if removed
374 : dl 1.55 */
375 :     boolean removeEq(Object o) {
376 : jsr166 1.68 for (int i = 0; i < size; i++) {
377 :     if (o == queue[i]) {
378 : dl 1.55 removeAt(i);
379 :     return true;
380 :     }
381 :     }
382 :     return false;
383 :     }
384 :    
385 : dholmes 1.11 /**
386 : jsr166 1.63 * Returns {@code true} if this queue contains the specified element.
387 :     * More formally, returns {@code true} if and only if this queue contains
388 :     * at least one element {@code e} such that {@code o.equals(e)}.
389 : dholmes 1.23 *
390 : dl 1.52 * @param o object to be checked for containment in this queue
391 : jsr166 1.63 * @return {@code true} if this queue contains the specified element
392 : dholmes 1.11 */
393 : dl 1.52 public boolean contains(Object o) {
394 : jsr166 1.68 return indexOf(o) != -1;
395 : tim 1.14 }
396 : dholmes 1.11
397 : dl 1.49 /**
398 : jsr166 1.63 * Returns an array containing all of the elements in this queue.
399 : dl 1.52 * The elements are in no particular order.
400 :     *
401 :     * <p>The returned array will be "safe" in that no references to it are
402 : jsr166 1.63 * maintained by this queue. (In other words, this method must allocate
403 : dl 1.52 * a new array). The caller is thus free to modify the returned array.
404 :     *
405 : jsr166 1.63 * <p>This method acts as bridge between array-based and collection-based
406 :     * APIs.
407 :     *
408 : jsr166 1.59 * @return an array containing all of the elements in this queue
409 : dl 1.49 */
410 : dl 1.52 public Object[] toArray() {
411 : dl 1.55 return Arrays.copyOf(queue, size);
412 : dl 1.52 }
413 : tim 1.2
414 : dl 1.52 /**
415 : jsr166 1.63 * Returns an array containing all of the elements in this queue; the
416 :     * runtime type of the returned array is that of the specified array.
417 :     * The returned array elements are in no particular order.
418 :     * If the queue fits in the specified array, it is returned therein.
419 :     * Otherwise, a new array is allocated with the runtime type of the
420 :     * specified array and the size of this queue.
421 : dl 1.52 *
422 :     * <p>If the queue fits in the specified array with room to spare
423 :     * (i.e., the array has more elements than the queue), the element in
424 :     * the array immediately following the end of the collection is set to
425 : jsr166 1.63 * {@code null}.
426 :     *
427 :     * <p>Like the {@link #toArray()} method, this method acts as bridge between
428 :     * array-based and collection-based APIs. Further, this method allows
429 :     * precise control over the runtime type of the output array, and may,
430 :     * under certain circumstances, be used to save allocation costs.
431 :     *
432 :     * <p>Suppose <tt>x</tt> is a queue known to contain only strings.
433 :     * The following code can be used to dump the queue into a newly
434 :     * allocated array of <tt>String</tt>:
435 :     *
436 : jsr166 1.72 * <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
437 : jsr166 1.63 *
438 :     * Note that <tt>toArray(new Object[0])</tt> is identical in function to
439 :     * <tt>toArray()</tt>.
440 : dl 1.52 *
441 :     * @param a the array into which the elements of the queue are to
442 :     * be stored, if it is big enough; otherwise, a new array of the
443 :     * same runtime type is allocated for this purpose.
444 : jsr166 1.63 * @return an array containing all of the elements in this queue
445 : dl 1.52 * @throws ArrayStoreException if the runtime type of the specified array
446 :     * is not a supertype of the runtime type of every element in
447 :     * this queue
448 :     * @throws NullPointerException if the specified array is null
449 :     */
450 :     public <T> T[] toArray(T[] a) {
451 :     if (a.length < size)
452 :     // Make a new array of a's runtime type, but my contents:
453 : dl 1.55 return (T[]) Arrays.copyOf(queue, size, a.getClass());
454 : jsr166 1.68 System.arraycopy(queue, 0, a, 0, size);
455 : dl 1.52 if (a.length > size)
456 :     a[size] = null;
457 :     return a;
458 : tim 1.1 }
459 : tim 1.2
460 : dholmes 1.23 /**
461 :     * Returns an iterator over the elements in this queue. The iterator
462 :     * does not return the elements in any particular order.
463 :     *
464 : dl 1.52 * @return an iterator over the elements in this queue
465 : dholmes 1.23 */
466 : tim 1.2 public Iterator<E> iterator() {
467 : dl 1.7 return new Itr();
468 : tim 1.2 }
469 :    
470 : dl 1.55 private final class Itr implements Iterator<E> {
471 : dl 1.7 /**
472 :     * Index (into queue array) of element to be returned by
473 : tim 1.2 * subsequent call to next.
474 : dl 1.7 */
475 : dl 1.55 private int cursor = 0;
476 : tim 1.2
477 : dl 1.7 /**
478 : dl 1.36 * Index of element returned by most recent call to next,
479 :     * unless that element came from the forgetMeNot list.
480 : dl 1.55 * Set to -1 if element is deleted by a call to remove.
481 : dl 1.7 */
482 : dl 1.55 private int lastRet = -1;
483 : dl 1.7
484 :     /**
485 : dl 1.55 * A queue of elements that were moved from the unvisited portion of
486 : dl 1.36 * the heap into the visited portion as a result of "unlucky" element
487 :     * removals during the iteration. (Unlucky element removals are those
488 : dl 1.55 * that require a siftup instead of a siftdown.) We must visit all of
489 : dl 1.36 * the elements in this list to complete the iteration. We do this
490 :     * after we've completed the "normal" iteration.
491 :     *
492 :     * We expect that most iterations, even those involving removals,
493 : jsr166 1.63 * will not need to store elements in this field.
494 : dl 1.36 */
495 : dl 1.55 private ArrayDeque<E> forgetMeNot = null;
496 : dl 1.36
497 :     /**
498 :     * Element returned by the most recent call to next iff that
499 :     * element was drawn from the forgetMeNot list.
500 :     */
501 : dl 1.55 private E lastRetElt = null;
502 :    
503 :     /**
504 :     * The modCount value that the iterator believes that the backing
505 : jsr166 1.63 * Queue should have. If this expectation is violated, the iterator
506 : dl 1.55 * has detected concurrent modification.
507 :     */
508 :     private int expectedModCount = modCount;
509 : dl 1.35
510 : dl 1.7 public boolean hasNext() {
511 : jsr166 1.56 return cursor < size ||
512 : dl 1.55 (forgetMeNot != null && !forgetMeNot.isEmpty());
513 : dl 1.7 }
514 :    
515 :     public E next() {
516 : dl 1.55 if (expectedModCount != modCount)
517 :     throw new ConcurrentModificationException();
518 : jsr166 1.56 if (cursor < size)
519 : dl 1.55 return (E) queue[lastRet = cursor++];
520 :     if (forgetMeNot != null) {
521 :     lastRet = -1;
522 :     lastRetElt = forgetMeNot.poll();
523 : jsr166 1.56 if (lastRetElt != null)
524 : dl 1.55 return lastRetElt;
525 : dl 1.36 }
526 : dl 1.55 throw new NoSuchElementException();
527 : dl 1.7 }
528 : tim 1.2
529 : dl 1.7 public void remove() {
530 : dl 1.55 if (expectedModCount != modCount)
531 :     throw new ConcurrentModificationException();
532 :     if (lastRet != -1) {
533 : dl 1.36 E moved = PriorityQueue.this.removeAt(lastRet);
534 : dl 1.55 lastRet = -1;
535 : jsr166 1.56 if (moved == null)
536 : dl 1.36 cursor--;
537 : dl 1.55 else {
538 : dl 1.36 if (forgetMeNot == null)
539 : dl 1.55 forgetMeNot = new ArrayDeque<E>();
540 : dl 1.36 forgetMeNot.add(moved);
541 : jsr166 1.56 }
542 : jsr166 1.63 } else if (lastRetElt != null) {
543 : dl 1.55 PriorityQueue.this.removeEq(lastRetElt);
544 : dl 1.36 lastRetElt = null;
545 : jsr166 1.63 } else {
546 :     throw new IllegalStateException();
547 : jsr166 1.68 }
548 : tim 1.2 expectedModCount = modCount;
549 : dl 1.7 }
550 : tim 1.2 }
551 :    
552 : tim 1.1 public int size() {
553 : tim 1.2 return size;
554 : tim 1.1 }
555 : tim 1.2
556 :     /**
557 : dl 1.52 * Removes all of the elements from this priority queue.
558 : dl 1.49 * The queue will be empty after this call returns.
559 : tim 1.2 */
560 :     public void clear() {
561 :     modCount++;
562 : dl 1.55 for (int i = 0; i < size; i++)
563 : tim 1.2 queue[i] = null;
564 :     size = 0;
565 :     }
566 :    
567 : dl 1.40 public E poll() {
568 : dl 1.36 if (size == 0)
569 : dl 1.40 return null;
570 : dl 1.55 int s = --size;
571 : dl 1.36 modCount++;
572 : jsr166 1.63 E result = (E) queue[0];
573 :     E x = (E) queue[s];
574 : dl 1.55 queue[s] = null;
575 :     if (s != 0)
576 :     siftDown(0, x);
577 : dl 1.36 return result;
578 :     }
579 :    
580 :     /**
581 : dl 1.55 * Removes the ith element from queue.
582 : tim 1.2 *
583 : dl 1.55 * Normally this method leaves the elements at up to i-1,
584 :     * inclusive, untouched. Under these circumstances, it returns
585 :     * null. Occasionally, in order to maintain the heap invariant,
586 :     * it must swap a later element of the list with one earlier than
587 :     * i. Under these circumstances, this method returns the element
588 :     * that was previously at the end of the list and is now at some
589 :     * position before i. This fact is used by iterator.remove so as to
590 : jsr166 1.63 * avoid missing traversing elements.
591 : tim 1.2 */
592 : dl 1.52 private E removeAt(int i) {
593 : jsr166 1.74 // assert i >= 0 && i < size;
594 : tim 1.2 modCount++;
595 : dl 1.55 int s = --size;
596 :     if (s == i) // removed last element
597 :     queue[i] = null;
598 :     else {
599 :     E moved = (E) queue[s];
600 : jsr166 1.56 queue[s] = null;
601 : dl 1.55 siftDown(i, moved);
602 : dl 1.36 if (queue[i] == moved) {
603 : dl 1.55 siftUp(i, moved);
604 : dl 1.36 if (queue[i] != moved)
605 :     return moved;
606 :     }
607 : dl 1.35 }
608 : dl 1.36 return null;
609 : tim 1.1 }
610 :    
611 : tim 1.2 /**
612 : dl 1.55 * Inserts item x at position k, maintaining heap invariant by
613 :     * promoting x up the tree until it is greater than or equal to
614 :     * its parent, or is the root.
615 :     *
616 :     * To simplify and speed up coercions and comparisons. the
617 :     * Comparable and Comparator versions are separated into different
618 :     * methods that are otherwise identical. (Similarly for siftDown.)
619 : jsr166 1.56 *
620 : dl 1.55 * @param k the position to fill
621 :     * @param x the item to insert
622 :     */
623 :     private void siftUp(int k, E x) {
624 : jsr166 1.56 if (comparator != null)
625 : dl 1.55 siftUpUsingComparator(k, x);
626 :     else
627 :     siftUpComparable(k, x);
628 :     }
629 :    
630 :     private void siftUpComparable(int k, E x) {
631 :     Comparable<? super E> key = (Comparable<? super E>) x;
632 :     while (k > 0) {
633 :     int parent = (k - 1) >>> 1;
634 :     Object e = queue[parent];
635 : jsr166 1.63 if (key.compareTo((E) e) >= 0)
636 : dl 1.55 break;
637 :     queue[k] = e;
638 :     k = parent;
639 :     }
640 :     queue[k] = key;
641 :     }
642 :    
643 :     private void siftUpUsingComparator(int k, E x) {
644 :     while (k > 0) {
645 :     int parent = (k - 1) >>> 1;
646 :     Object e = queue[parent];
647 : jsr166 1.63 if (comparator.compare(x, (E) e) >= 0)
648 : dl 1.55 break;
649 :     queue[k] = e;
650 :     k = parent;
651 :     }
652 :     queue[k] = x;
653 :     }
654 :    
655 :     /**
656 :     * Inserts item x at position k, maintaining heap invariant by
657 :     * demoting x down the tree repeatedly until it is less than or
658 :     * equal to its children or is a leaf.
659 :     *
660 :     * @param k the position to fill
661 :     * @param x the item to insert
662 :     */
663 :     private void siftDown(int k, E x) {
664 : jsr166 1.56 if (comparator != null)
665 : dl 1.55 siftDownUsingComparator(k, x);
666 :     else
667 :     siftDownComparable(k, x);
668 :     }
669 :    
670 :     private void siftDownComparable(int k, E x) {
671 :     Comparable<? super E> key = (Comparable<? super E>)x;
672 :     int half = size >>> 1; // loop while a non-leaf
673 :     while (k < half) {
674 :     int child = (k << 1) + 1; // assume left child is least
675 :     Object c = queue[child];
676 :     int right = child + 1;
677 :     if (right < size &&
678 : jsr166 1.63 ((Comparable<? super E>) c).compareTo((E) queue[right]) > 0)
679 : dl 1.55 c = queue[child = right];
680 : jsr166 1.63 if (key.compareTo((E) c) <= 0)
681 : dl 1.55 break;
682 :     queue[k] = c;
683 :     k = child;
684 :     }
685 :     queue[k] = key;
686 :     }
687 :    
688 :     private void siftDownUsingComparator(int k, E x) {
689 :     int half = size >>> 1;
690 :     while (k < half) {
691 :     int child = (k << 1) + 1;
692 :     Object c = queue[child];
693 :     int right = child + 1;
694 :     if (right < size &&
695 : jsr166 1.63 comparator.compare((E) c, (E) queue[right]) > 0)
696 : jsr166 1.56 c = queue[child = right];
697 : jsr166 1.63 if (comparator.compare(x, (E) c) <= 0)
698 : dl 1.55 break;
699 :     queue[k] = c;
700 :     k = child;
701 : tim 1.2 }
702 : dl 1.55 queue[k] = x;
703 : dl 1.36 }
704 : dl 1.35
705 : dl 1.36 /**
706 :     * Establishes the heap invariant (described above) in the entire tree,
707 :     * assuming nothing about the order of the elements prior to the call.
708 :     */
709 :     private void heapify() {
710 : jsr166 1.56 for (int i = (size >>> 1) - 1; i >= 0; i--)
711 : jsr166 1.63 siftDown(i, (E) queue[i]);
712 : tim 1.2 }
713 :    
714 : dholmes 1.23 /**
715 : dl 1.52 * Returns the comparator used to order the elements in this
716 : jsr166 1.63 * queue, or {@code null} if this queue is sorted according to
717 : dl 1.52 * the {@linkplain Comparable natural ordering} of its elements.
718 :     *
719 :     * @return the comparator used to order this queue, or
720 : jsr166 1.63 * {@code null} if this queue is sorted according to the
721 :     * natural ordering of its elements
722 : dholmes 1.23 */
723 : tim 1.16 public Comparator<? super E> comparator() {
724 : tim 1.2 return comparator;
725 :     }
726 : dl 1.5
727 :     /**
728 : jsr166 1.77 * Saves this queue to a stream (that is, serializes it).
729 : dl 1.5 *
730 :     * @serialData The length of the array backing the instance is
731 : jsr166 1.63 * emitted (int), followed by all of its elements
732 :     * (each an {@code Object}) in the proper order.
733 : dl 1.5 */
734 : dl 1.22 private void writeObject(java.io.ObjectOutputStream s)
735 : jsr166 1.75 throws java.io.IOException {
736 : dl 1.7 // Write out element count, and any hidden stuff
737 :     s.defaultWriteObject();
738 : dl 1.5
739 : jsr166 1.63 // Write out array length, for compatibility with 1.5 version
740 :     s.writeInt(Math.max(2, size + 1));
741 : dl 1.5
742 : jsr166 1.64 // Write out all elements in the "proper order".
743 : jsr166 1.63 for (int i = 0; i < size; i++)
744 : dl 1.5 s.writeObject(queue[i]);
745 :     }
746 :    
747 :     /**
748 : jsr166 1.77 * Reconstitutes this queue from a stream (that is, deserializes it).
749 : dl 1.5 */
750 : dl 1.22 private void readObject(java.io.ObjectInputStream s)
751 : dl 1.5 throws java.io.IOException, ClassNotFoundException {
752 : dl 1.7 // Read in size, and any hidden stuff
753 :     s.defaultReadObject();
754 : dl 1.5
755 : jsr166 1.63 // Read in (and discard) array length
756 :     s.readInt();
757 :    
758 : jsr166 1.68 queue = new Object[size];
759 : dl 1.5
760 : jsr166 1.64 // Read in all elements.
761 : jsr166 1.63 for (int i = 0; i < size; i++)
762 :     queue[i] = s.readObject();
763 : jsr166 1.64
764 : jsr166 1.68 // Elements are guaranteed to be in "proper order", but the
765 :     // spec has never explained what that might be.
766 :     heapify();
767 : dl 1.5 }
768 : tim 1.1 }

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